The present invention generally relates to equipment and processes used in the commercial printing industry. More particularly, this invention relates to a web coating apparatus and method suitable for use in inline and offline web-fed finishing systems used in the commercial web printing industry.
Various types of coating (printing) machines are known and used in the commercial offset web industry. A particular type of coating machine is adapted to transfer a liquid coating to a pre-printed substrate, referred to as a web, formed of a suitable material, for example, paper. The coating process often uses a rotary-style coating machine that includes a coating cylinder (for example, an anilox roller) having a cylindrical outer surface to which a coating is applied as the coating cylinder rotates. A doctor blade assembly is typically used with an anilox roller to remove excess coating from the surface of the coating cylinder, to ensure that the coating cylinder carries a relatively uniform layer of coating on its cylindrical surface. The coating may be applied to the coating cylinder through contact with a second cylinder that is partially submerged in the coating within a reservoir, or directly applied by partially submerging the coating cylinder in the coating. Another alternative is to apply the coating using an enclosed coating chamber that incorporates the doctor blade assembly. The coating cylinder transfers the coating to a rotating fixed repeat-sized plate cylinder (roller), which in turn carries the coating to the web. The plate cylinder carries a raised pattern such that the coating transferred to the plate cylinder will form the desired coating on the web, for example, a gloss or mat finish. The transfer of coating from the plate cylinder to the web occurs at a printing nip between the plate cylinder and a rotating impression cylinder (roller). Once the printed web has traveled away from the printing nip, the coating on the web is cured, for example, using an ultraviolet (UV) curing lamp system. One or more optional “chill rolls” may be placed at the exit of the curing system to help remove excess temperature from the web and control the tension in the web downstream of the curing process.
Rotary-style coating machines of the type described above have been historically limited to applying a very narrow range of coatings, such as “gloss coatings,” to substrates. The narrow range of coatings is inherently due to the coating cylinder having a fixed anilox construction. While certain coating machines are described as having a removable and/or changeable coating cylinder, the process requires the removal of the complete coating cylinder from the machine, resulting in an extensive process of uncoupling the drive train and unbolting and lifting heavy cylinders. This process is typically very costly, time consuming and potentially unsafe, with the result that many in the printing industry do not remove and replace coating cylinders.
Rotary-style coating machines are also typically dedicated to a plate cylinder having a certain circumference size (referred to as fixed press repeat), with all cylinders of the machine, with the exception of any optional chill rolls, driven together by a single motor or mechanical drive train. A drawback of all cylinders being driven together is the inability to change the repeat (circumference size) of the plate cylinder without making gearing changes. The result is that typical coating machines are dedicated to a fixed size printing press application matching a single image repeat.